Various portable generators have been proposed, to be moored in and powered by flowing water, to generate electricity that is usable at that location. Thus, a typical unit might be used in a river or stream having currents only of the order of 5-25 feet per second. The energy pick-up means, an impeller or propeller driven by the current, may be designed to operate efficiently off of kinetic energy conversion and/or off of potential energy conversion. However, as the total unit energy level will be relatively small, even a slight increase in the efficiency of the energy pick-up means becomes significant.
One type of portable generator is illustrated in the McLaughlin Pat. No. 868,798, having a generator mounted within a water-tight housing, and a shaft extended through seals in the housing and connected internally to the generator and externally to a propeller. The portable generator is moored by flexible nonextendable lines secured to separate anchors, to allow the generator to drag freely and directly in the water, and the water flows around the generator housing and over and through the propeller to generate electrical power.
A modified version of this type of portable generator is illustrated in the Souczek Pat. No. 2,501,696, where several generator housings are used, connected together on a winged structure; and the wing structure is connected to the anchored lines. The wing structure is operated to fly in the flowing water, to relocate the unit to different debths in the stream, as needed for passing vessels or the like. Another modified version of this type is illustrated in the Wracsaricht Pat. No. 4,306,157, where several multi-blade propellers are used.
Another type of portable generator is illustrated in the Vary et al Pat. No. 3,980,894, which has an open-ended flow tube, and the impeller and generator housing are mounted within the flow tube, to be actuated by the water flowing therethrough. One modified version further has ports midway along the tube that open toward a second set of impeller blades, and a scoop on the tube is used to direct water flow through these ports to impact against the second blades.
In each of these designs, the velocity of the water passing over the propeller is the same as or close to the velocity or actual current of the river or stream.